T(Z) DIAGRAM AND OPTICAL ENERGY GAP VALUES OF ZN1-ZMNZGA2SE4 ALLOYS

摘要

The T(z) diagram of the system Zn1-zMnzGa2Se4 was obtained from X-ray diffraction and differential thermal analysis measurements. It was found that at lower temperatures, a single phase solid solution occurs across the whole composition range and values of the lattice parameters were determined as a function of z. At higher temperatures, an order-disorder transition occurs to what is probably a partially ordered tetragonal structure when 0 < z < 0.83, and to a disordered defect zinc-blende structure when 0.83 < z < 1.0. In the T(z) diagram, it is found that all of the phase boundaries show discontinuities at z approximate to 0.83. Although the two terminal compounds have very similar tetragonal structures, they have different space group symmetries, and hence the discontinuities at z approximate to 0.83 are attributed to an abrupt change in space group symmetry at this composition. The values of the optical energy gap are found to show a similar discontinuity at the same composition. Two other similar alloy systems have recently been found to show similar behavior, and the results for the three systems are compared. (C) 1995 Academic Press, Inc. [References: 15]